Lysophospholipase (LPL) is a widely distributed enzyme which regulates intracellular lipids and occurs in numerous isoforms. These isoforms vary in molecular mass, substrate metabolized, and optimum pH required for activity. Small isoforms, approximately 15-30 kD, function as hydrolases; large isoforms, those exceeding 60 kD function both as transacylases and hydrolases. LPLs are regulated by lipid factors such as acylcarnitine, arachidonic acid and phosphatidic acid.
Sugimoto, H. et al. (1996; J. Biol. Chem. 271:7705-11) isolated a monomeric, 24 kD LPL from rat liver which hydrolyzed lysophosphatidylcholine, lysophosphatidylethanol-amine, lysophosphatidylinositol, lysophosphatidylserine, and 1-oleoyl-2-acetyl-sn-glycero-3-phosphocholine at pH 6-8.0. In an assay measuring LPL hydrolysis of 1-palmitoyl-glycero-3-phosphocholine, the substrate dependence curve was sigmoidal, the enzyme was active from pH 5.5-9.0, and activity was not affected by Ca.sup.2 +, Mg.sup.2 +, or EDTA. Km and Vmax were calculated to be 0.17 mM and 1.55 .mu.M/min/mg, respectively.
The cDNA for rat liver LPL was isolated, and the deduced amino acid sequence showed a conserved GXSXG motif and similarity to esterases from Pseudomonas fluorescence and Spirulina platensis. Transcripts encoding rat liver LPL were isolated from spleen, heart, brain, lung, stomach, testis, and liver. Experiments showed that DMSO treatment of an HL-60 (myelocytic leukemia) cell line induced granulocyte differentiation, produced a 3-fold increase in the amount of enzyme, and correlated with the release of arachidonic acid.
The role of LPLs in human tissues has been investigated in various research studies. Selle, H. et al. (1993; Eur. J. Biochem. 212:411-16) characterized the role of LPL in the hydrolysis of lysophosphatidylcholine which causes lysis in erythrocyte membranes. Similarly, Endresen, M. J. et al. (1993) Scand. J. Clin. Invest. 53:733-9) reported that the increased hydrolysis of lysophosphatidylcholine by LPL in pre-eclamptic women causes release of free fatty acids into the sera. In renal studies, LPL was shown to protect NA+,K+-ATPase from the cytotoxic and cytolytic effects of cyclosporin A (Anderson, R. et al. (1994) Toxicol. Appl. Pharmacol. 125:176-83).
The discovery of a new human lysophospholipase and the polynucleotides encoding it satisfies a need in the art by providing compositions which are useful in the diagnosis, prevention and treatment of inflammation and disorders associated with immune response and cell proliferation.